1. Field of the Invention
The present invention relates to a magnetic recording/reading apparatus of a rotary head type (such as a VTR or DAT) provided with a double azimuth head, and drum and head arrangement used for the magnetic recording/reading apparatus.
2. Description of Related Art
Recently, a trend has been toward a so-called guard bandless recording system in which a clearance called a guard band is not provided between adjacent tracks in order to enhance a recording density for a magnetic recording/reading apparatus such as a VTR and DAT.
Guard bandless recording adopts a principle that crosstalk from an adjacent track due to azimuth loss in regeneration is reduced by differentiating the angle of a head gap, i.e., a so-called azimuth angle of two heads for recording or reading data in adjacent tracks. Further, guard bandless recording is a system in which data for two tracks are simultaneously recorded or read by specifying a high frequency for a recording signal to realize high density recording. Provided are two heads (called a double azimuth head) which are closely arranged, and the azimuth angle of which is different and which has a split wideband signal associated therewith. The reason why a signal is split is because if a non-split signal of the same capacity is recorded, a recording frequency is required to be doubled and an output is deteriorated due to a high frequency loss. A method of rotating a rotating drum at a double speed is also conceivable. However, problems such as a deterioration of head contact performance and a reduction of the life of a head occur.
Further, for the above double azimuth head, an additional problem occurs in that a range of setting tape/head contact conditions in which a satisfactory output can be obtained is small. That is, the range of conditions for enhancing contact between a head and a tape (so-called stabilizing head contact) is narrowed.
To solve such a problem, one attempt for obtaining the most suitable head contact performance by specifying a width of a core on opposite sides of two heads of a double azimuth head is disclosed in, for example, the Japanese published unexamined patent application No. H2-149908 reference.
If data for two tracks are simultaneously recorded or read by a double azimuth head, a predetermined difference in level (i.e., head shift or displacement) is required to be provided in a direction perpendicular to the rotational direction of a rotating drum, so that a predetermined track width is formed between a preceding head and a succeeding (i.e., adjacent) head in the rotational direction of the rotating drum. In this case, as the diameter of a rotating drum is as small as 40 mm and 30 mm in a small-sized system such as an 8 mm video tape recorder and DAT, a pair of heads arranged in the drum are required to be closely arranged in a configuration of a preceding head and a succeeding head. For example, if a pitch between adjacent tracks is 15 .mu.m, a difference in level (i.e., head shift or displacement) between the preceding head and the succeeding head is required to be approximately 15 .mu.m and a distance between gaps of the preceding head and the succeeding head is required to be 1 mm or less to eliminate a time lag between signals of each channel.
If the preceding head and the succeeding head are arranged closely as described above, several problems have been found to occur. More particularly, a head gap is not located at a top of a tape portion which envelops a head and thus a head/tape contact location occurs differently from the case of a single head. Further, a face pressure at a gap is reduced because a width in which a tape and a head are in contact is wider than that of a single head, and as a result of the foregoing, it is difficult to secure a satisfactory head contact performance. As an example, a phenomenon occurs wherein a deformation of a tape by a preceding head has an effect on a succeeding head and contact performance between the succeeding head and the tape is deteriorated. More particularly, on a side of an exit from a drum which is on an upstream side of a tape, an upper end of the tape is scanned by a head. However, as there is no regulation at the upper edge of a tape, a succeeding head is susceptible to the effect of the deformation of a tape by a preceding head. Therefore, head contact performance varies depending upon the location of a head gap and the form (e.g., shape) of the end of a head.
Therefore, there is a problem that reliable required head contact performance cannot be obtained stably by only specifying the width of a core as disclosed in the above reference.
As additional related references, JP 62-192906 describes a single head having a single radius and a cut-off portion formed by a linear shape, JP 2-149908 describes double azimuth heads and a width and length of head tips thereof, and Japanese published unexamined patent application No. H2-193308 likewise relates to a head structure.
In summary, if heads are protruded by the same quantity and the tension of a tape is equal, the pressure of the tape on the heads is fixed. However, the length in which a head and a tape are in contact varies depending upon the form (e.g., shape) of the end of the head, particularly a radius of curvature in the rotational direction.
The contact length of a tape is reduced by reducing the radius of curvature of a head and head touch can be stabilized by increasing contact pressure of a tape on a head. However, although contact performance is enhanced by reducing the radius of curvature of a head and increasing the contact pressure of a tape, a resultant problem occurs in that the abrasion of the head is promoted and the head becomes weak over time.